Ford lehman 120 #6 cylinder

[Whgoffrn]

I've just purchased a 37' trawler with a single lehman 120 and while it runs good now I plan to do maintenance on it and protect from future problems.....from all I've read the Lehman's seem to be good engines as long as you do proper maintenance but 1 common problem I see is cylinder 6 getting hot and destroying piston .....besides making sure there is proper clean oil in the engine and its getting good water and the heat exchangers are working good..... is there any after market products or ways to ensure that #6 cylinder stays cool to protect it?

 

[Comodave]

Yes, it is a known problem. I am not sure if there is anything to do about it, maybe make sure you have a good impeller so you get max water flow. I would call Brian at American Diesel. He is the Lehman guru and has always been helpful to me. 804-435-3107

 

[Busterbrown]

Expansion Tank Neck & Recovery System
https://img1.wsimg.com/blobby/go/ad...wners Sheet 120 & 80 HP.pdf?ver=1584478468913

 

[jleonard]

I think flushing the antifreeze cooling system and having fresh coolant is also important

 

[DavidM]

The classical problem with in line 6 cylinder engines is that the #6 cylinder develops an air pocket that limits coolant flow and allows it to overheat. American Diesel's Expansion Tank Neck and Recovery system should minimize that problem.

But talk to American Diesel about it. They are the Lehman pros.

David

 

[Whgoffrn]

I think flushing the antifreeze cooling system and having fresh coolant is also important

I'm not sure if some lehman trawlers have closed systems with a radiator ? Or how that works but ours is raw water from river/ocean through strainer into impeller water pump block oil and transmission coolers and back out exhaust so no antifreeze in system just river or ocean water

 

[Whgoffrn]

The classical problem with in line 6 cylinder engines is that the #6 cylinder develops an air pocket that limits coolant flow and allows it to overheat. American Diesel's Expansion Tank Neck and Recovery system should minimize that problem.

But talk to American Diesel about it. They are the Lehman pros.

David

And ty on the tip about the expansion tank neck ....I vaguely understand how the cooling system works in the lehman raw water comes in goes through a strainer then to impeller / water pump block oil coolers transmission coolers and back out the exhaust but I sorta don't understand the purpose of the expansion tank neck and recovery system ....its my vague misunderstanding of how the cooling system operates that I cant wrap my head around how that would help that #6 cylinder but ty for the tip and I'll call AD maybe they can explain it.

 

[kchace]

I have never heard of a Ford Lehman with only raw water cooling, but if you have one then the expansion tank wouldn’t really serve a purpose.

Do you not have a good sized heat exchanger on the back of the engine? It would be about 3-4” in diameter and maybe 16” long?

Ken

 

[Pete Meisinger]

It is two different possibilities you are talking about. Consider these two summaries:neither are really true but #2 is closer than #1
FIRST: The #6 cylinder often overheats and ruins F.L. engines
VS
SECOND:When a F.L. fails, it is often the #6 cylinder.

F.L. 120's seldom, rarely, almost never have a catastrophic failure. Keep your impellers in good condition. When one does fail make sure you get all the pieces out of the engine. I guess changing the antifreeze occasionally wouldn't hurt. Watch your temp gauge.

Don't worry about Ole #6

pete

 

[otnot]

Some where I have read that there is a way to route more cooling to the #6 cylinder??? I can't find the reference.

 

[Whgoffrn]

I have never heard of a Ford Lehman with only raw water cooling, but if you have one then the expansion tank wouldn’t really serve a purpose.

Do you not have a good sized heat exchanger on the back of the engine? It would be about 3-4” in diameter and maybe 16” long?

Ken

Ok yeah it's my misunderstanding of how the cooling system works ...I thought it was just raw straight water going through the engine when I guess I misunderstood how it works there is antifreeze in the engine and the raw water passes by the antifreeze to cool it down....I totally misunderstood how it worked I was thinking the heat exchanger was raw water passing by hot oil to cool the oil down ....so my bad yes there is coolant lol it's just me being new to the lehman 120 and not fully understanding it all just yet

 

[cdsailor]

The classical problem with in line 6 cylinder engines is that the #6 cylinder develops an air pocket that limits coolant flow and allows it to overheat. American Diesel's Expansion Tank Neck and Recovery system should minimize that problem.

But talk to American Diesel about it. They are the Lehman pros.

David

Are you saying that the air pocket issue around #6 cannot be avoided or remedied WITHOUT the AD recovery system? What's the mechanism of the fault?

Thanks.

 

[Caphenning]

I've just purchased a 37' trawler with a single lehman 120 and while it runs good now I plan to do maintenance on it and protect from future problems.....from all I've read the Lehman's seem to be good engines as long as you do proper maintenance but 1 common problem I see is cylinder 6 getting hot and destroying piston .....besides making sure there is proper clean oil in the engine and its getting good water and the heat exchangers are working good..... is there any after market products or ways to ensure that #6 cylinder stays cool to protect it?

The best thing you can do towards operational reliability is pull an oil sample after taking a run on oil that has at least 25 hours on it (optimum is to have it at the end of the interval you plan to use to change oil or filter) and send it to Blackstone Labs for analysis and to start your baseline. They will be able to tell you about that piston getting hot, or bearings wearing through, cams or injector pump wear/spalling... before you get to the the failure point, indeed you find out when the problem will be the very cheapest possible to fix.

 

[Nomad Willy]

Could one drill and tap a hole in the back of the block (where #6 cyl. is) and route it back to the water pump intake. Using a bronze threaded to hose barb fitting should be fairly easy to install. Coolant flow over all the cylinders should increase. And if the hole/fitting is high enough the air would be pumped out as well.
One could use a mini version say 1/4” just to deal w the air collecting at #6.

A bit if research may turn up other solutions as many/most engines are hot at the rear cylinder. How do other people cope when it becomes a problem?
You may find (for example) that most engines extend the water jacket aft a bit to provide extra coolant volume ..... ???

Buying a boat w a Perkins engine is another thought.

 

[Whgoffrn]

I talked to the guys at A.D about it and they said it's not nearly as common as what message forums claim....they said when that happens there are other warning signs that are often ignored like other cylinders getting hot first ...kinda makes some sense why would cylinder 1 be 180 and number 6 be 300 yes im sure number 6 can be warmer than the others if clogged but the other cylinders would get warmer also....I talked to them about putting an sensor at #6 and they said that may help but it would be mounted external and have some variances in temp and may or may not be a good indicator if there was a problem...I asked about routing more fluid to 6 and also makes sense that what I route to 6 gets routed away from another cylinder so now I may have new issues at a different cylinder....they said as long as coolant was flushed regularly and I had good water flow and that I paid attention to heat temp gauge I should never have a problem so I guess I'll just go with that...
I may get the expansion tank at some point in hopes that maybe if there was an air bubble in 6 jacket maybe it would come up into the expansion tank....not completely sure I understand how the expansion tank would help serve to eliminate that issue

 

[Caphenning]

Could one drill and tap a hole in the back of the block (where #6 cyl. is) and route it back to the water pump intake. Using a bronze threaded to hose barb fitting should be fairly easy to install. Coolant flow over all the cylinders should increase. And if the hole/fitting is high enough the air would be pumped out as well.
One could use a mini version say 1/4” just to deal w the air collecting at #6.

A bit if research may turn up other solutions as many/most engines are hot at the rear cylinder. How do other people cope when it becomes a problem?
You may find (for example) that most engines extend the water jacket aft a bit to provide extra coolant volume ..... ???

Buying a boat w a Perkins engine is another thought.

No, what one would do is pull the head and drill through a new passage set through the block deck and head, joining the water jackets and providing normalized flow.

 

[hytedin]

Used this to fill my SP275 after overhaul.


https://www.harborfreight.com/cooling-system-test-and-refill-kit-64985.html

 

[SoWhat]

An EGT sensor would probably give you quicker warning of overheating condition than block sender. If you were totally OCD you could attach thermocouples near each injector.

 

[catalinajack]

Borel Manufacturing.

An EGT sensor would probably give you quicker warning of overheating condition than block sender. If you were totally OCD you could attach thermocouples near each injector.

 

[BruceK]

I have never heard of a Ford Lehman with only raw water cooling, but if you have one then the expansion tank wouldn’t really serve a purpose....Ken

There were several IG32s here with twin 4cyl Lehmans directly sea water cooled. We looked at one, broker started the engines, some odd bits of stuff(?shell) came out of the exhaust.

 

[syjos]

I flush and reverse flush the FL around every ten years with with fresh water after a Prestone Radiator Flush treatment using a "T" in the water heater loop. That keeps sediment from accumulating in coolant passage corners and small passages clear. I did the same with previous boats Perkins 6.3544.

Plus I do laser gun temperature checks on various places on the engine during the spring shakedown cruise and weekly during the summer cruise.

I'm due for a Flush and will try to document the process with pictures.

 

[Nomad Willy]

Caphenning wrote;
“ No, what one would do is pull the head and drill through a new passage set through the block deck and head, joining the water jackets and providing normalized flow.”

Sounds good to me.
How big (dia.) of a hole could be had?
How does the coolant flow in the block and head? Gotta have equal volume flowing both ways. That must be hard to do in a 6 cyl in-line engine. Must go down one side of the block and back on the other.

 

[Mako]

How old is the boat? 10 years, 20 years, 30 years? Has #6 overheated in all that time?

Perhaps keep running it at reasonable loads and don't worry about it.

 

[SteveK]

AD says it is not all that common as stated in forums. (as previously posted). Another thread talks about bleeding the air with the petcock at #1 in the exhaust manifold. Is there a relation to the #6 problem if air is not bled?

 

[syjos]

AD says it is not all that common as stated in forums. (as previously posted). Another thread talks about bleeding the air with the petcock at #1 in the exhaust manifold. Is there a relation to the #6 problem if air is not bled?

I bleed that petcock at the high end of the manifold every morning while cruising. I don't know how air gets in there but there is always air present.

An overflow tank will not get air out of the manifold. The petcock is the high spot for air to accumulate. I'm thinking about replacing the petcock on the manifold with a hose barb and connecting it to the bottom of the engines expansion tank with hose which may create a shortcut for air to escape.

From talking to Brian and other Lehman "experts" the #6 cylinder overheat issue is not as common as previously stated. I laser gun it often and the temperature there is not higher than others.

 

[SteveK]

I bleed that petcock at the high end of the manifold every morning while cruising. I don't know how air gets in there but there is always air present.

An overflow tank will not get air out of the manifold. The petcock is the high spot for air to accumulate. I'm thinking about replacing the petcock on the manifold with a hose barb and connecting it to the bottom of the engines expansion tank with hose which may create a shortcut for air to escape.

From talking to Brian and other Lehman "experts" the #6 cylinder overheat issue is not as common as previously stated. I laser gun it often and the temperature there is not higher than others.

IMO leading that petcock to the underside of expansion tank is not a good idea. I think it will interfere with normal circulation the same as if opened while engine is running.

 

[Lepke]

In the old days when racers still ran 6 cylinder inline engines, a number of small changes were made to increase the coolant going by the back cylinder.

After a test run to measure individual cylinder temps, some block and head water passages were slightly restricted in some of the forward cylinders so more flow was available to #6. Also more blades were added to the coolant pump impeller to move more water. Thermostats and housings were modified to allow a greater flow. On some engines, the water jacket of #6 was tapped and a line run to the radiator, bypassing the thermostat and allowing more flow to #6. The line had a valve used when warming the engine. And some taped a line from the coolant pump directly to #6. Thermostats are restrictive even when all the way open. There may be a racing thermostat that fits with a much bigger opening.
I don't know Lehman that well, but a higher hp Lehman may have a higher volume coolant pump that fits. Detroit pumps look the same on the outside, but the impeller is different depending on the hp.

 

[syjos]

IMO leading that petcock to the underside of expansion tank is not a good idea. I think it will interfere with normal circulation the same as if opened while engine is running.

That is one of the issues why I have not done it yet. The engines expansion tank is under the same pressure as the coolant in the manifold so it will be within the confines of the closed system. However, the shortcut created by the hose from manifold to tank may create interference as you stated or a separate coolant loop. The petcock diameter is a little over 1/4" so the volume of coolant would be small.

The coolant is ready for flush and replace so I might experiment when I do that. If I do the mod, I'll use a high temp clear hose to monitor flow.

Opening the petcock to bleed air has not been a big deal.

 

[BruceK]

If I remember the Manual correctly, opening the petcock was advised when topping up coolant. Rarely if ever did air bleed instead of coolant. If you are getting air accumulation daily when cruising something seems amiss.

 

[SteveK]

That is one of the issues why I have not done it yet. The engines expansion tank is under the same pressure as the coolant in the manifold so it will be within the confines of the closed system. However, the shortcut created by the hose from manifold to tank may create interference as you stated or a separate coolant loop. The petcock diameter is a little over 1/4" so the volume of coolant would be small.

The coolant is ready for flush and replace so I might experiment when I do that. If I do the mod, I'll use a high temp clear hose to monitor flow.

Opening the petcock to bleed air has not been a big deal.

It is said not to open when engine is running as it will suck in air. If you did plumb to expansion tank bottom it would suck fluid, that would bypass the thermostat?